TRANSFORMATION BEHAVIOR OF Ti50-x/2Ni50-x/2Cux ALLOYS

1.IntroductionIt is known that transformation behavior of Ti50Ni50-xCux shape memory alloys depends on the Cucontent[1-3].When the substitution of Cu for Ni is less than5at.%,the alloy transforms similar to that ofthe equiatomic Ti-Ni alloy,i.e.,from cubic(B2)to monoclinic(B19′).When the substitution of Cureaches10at.%,the alloy transforms in two stages,i.e.,from cubic(B2)to orthorhombic(B19),and thenfrom orthorhombic to monoclinic(B19′).By further substitution exceeding20at.%,the allo…     

Transformation behavior and shape memory effect of Ti50-xNi48Fe2Nbx alloys by aging treatment

The influence of aging treatment on transformation behavior and shape memory of the Ti50-xNi48Fe2Nbx(x=0,0.6,0.8,1.0,and 1.2)alloys was investigated using differential scanning calorimeter(DSC),mechanical drawing machine,and microhardness tester in this paper.It is indicated that the aging treatment has a significant effect on the phase transformation temperatures(Ms,Mf,Mp,As,Af,and Ap)and microhardness of the samples.The phase transformation temperatures are found to decrease initially with the increasing aging temperature from 300 to 500 ℃ and increase with further increase of the aging temperature.The aging treatment at intermediate temperature between 400 and 500 ℃ results in an improved shape memory effect.In addition,the highest microhardness value is also obtained.     

固溶态Ti（50＋x）Pd30Ni（20—x）合金中的相变特征

Ti(50 x)Pd30Ni(20-x)合金在固溶处理之后存在2次相变，使用DSC，XRD，DMTA以及TEM等手段研究了这种相变，结果表明，低温马氏体为单斜的B19'相，而高温母相则为体心立方的B2相，在相变过程中点阵的切变以正交的B19马氏体相作为过渡。低温马氏体的弹性模量比高温奥氏体的弹性模量高10GPa。随着频率减小，阻尼增大。在较高的频率下，弹性模量曲线和阻尼曲线对于过渡相的存在反映不明显，室温下马氏体为细狭的板条状，当温度达773K时，合金中有明显的析出物产生。     

Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns.     

Microstructure and transformation behavior of Ni50Ti45Ta5 shape memory alloy

1　INTRODUCTIONTheNiTishapememoryalloy (SMA )iscur rentlyatopicofnotableinterestinmedicine .Itpro videsauniqueopportunitytomakenovelsurgicalim plantsandinstrumentsforminimallyinvasive ,vascu larandorthopedicsurgery .Recently ,NiTiimplantshavebeendevelopedforcardiovascularandgastroin testinalsurgery[13] .ThehighnickelcontentofNiTi(5 4%bymass)cancauseproblemsinbiocompati bilitybecauseoftoxiceffectsofnickel[4 ] .Moreover ,thelowX rayvisibilityofNiTiSMAhaslimitedsomemedicalapplications …     

Ti49.8Ni50.2合金丝材的热机械循环疲劳和相变研究

研究了热处理对Ti49.8Ni50.2合金丝材的相变、力学性能以及热机械循环疲劳的影响.结果表明:随着退火温度的升高,R→B19'相变温度升高,B2→R相变温度降低,873 K退火时B2→R和R→B19'相变重合.当退火温度(Ta)低于823 K时,试样处于回复阶段,σM随退火温度升高有小幅度下降,723 K退火试样在热机械循环中获得最大稳定回复应变, 疲劳寿命随退火温度的升高略有提高;退火温度高于823 K时,试样发生再结晶,σM剧烈下降,稳定回复应变剧烈降低,而疲劳寿命由103升至104数量级.     

Transformation behaviors of Ti48.5Ni48Fe2Nb1.5 dependence of annealing and thermomechanical cycling

The effect of annealing treatments and thermomechanical cycling on the transformation behaviors and shape memory effect of Ti48.5Ni48Fe2Nb1.5 shape memory alloys were investigated using electrical resistivity measurement and tensile testing. It is found that the transformation behaviors are influenced considerably by the annealing treatments. Both Ms and As increase with increasing annealing temperature and cooling rate. Martensite stabilization occurs during thermomechanical cycles, thus resulting in lower...     

A wide temperature window for the magnetostructural transformation in Mn50Ni50-x-ySnxCoy alloys

In order to open a wide temperature window for a magnetostructural transformation, Sn–Co co-doping was explored in the Mn₅₀Ni₅₀ alloy. The experimental results show that doping with Sn and doping with Co have different effects on the martensitic and austenitic structures, the martensitic transformation, the thermal hysteresis and the magnetic properties of the martensitic and austenitic phases. By tuning the Sn and Co content in Mn₅₀Ni_50−x−ySn_xCo_y from x = 11, y = 0 to x = 6, y = 14, the martensitic transformation temperature, T_m, could be adjusted over the range from 99 K to 450 K, with the condition that T_m remains lower than the Curie temperature of the austenitic phase, Tc^a, which varied from 288 K to 565 K. Thus, a 351 K temperature window for the magnetostructural transformation was established and a series of ferromagnetic shape memory alloys was identified.     

Magnetic properties and phase diagram of Ni50Mn50−xGax ferromagnetic shape memory alloys

We present the magnetic properties and the magnetic phase diagram of Ni₅₀Mn_50?xGa_x ferromagnetic shape memory alloys across a wide concentration range. Martensitic transformation, intermediate transformation, B2–L2₁ order–disorder transformation, Néel and Curie temperatures are determined for the prepared samples. The martensitic transformation temperature decreases with increasing Ga concentration and bends two times when crossing the Curie temperature and the intermediate-phase transformation temperature. Spontaneous magnetization and its composition dependence were also investigated. Composition dependence of the transformation temperatures and the spontaneous magnetization in the martensite phase of Ni₅₀Mn_50?xGa_x are compared with those of Ni₅₀Mn_50?xIn_x and Ni₅₀Mn_50?xSn_x, revealing a similarity in the NiMn-based alloy systems.     

热处理对CuAlBe形状记忆合金组织和相变行为的影响

采用DSC法和电阻法测定了CuAlBe形状记忆合金的相变点,并通过组织观察和性能(硬度)测定等方法,综合分析研究了热处理工艺对其组织和相变行为的影响。结果表明,热处理对合金的晶粒大小和相变点影响较大,加热温度高和保温时间长都会使晶粒长大、相变点升高。热循环使相变行为的稳定性提高。低温时效会使相变点降低;而高温时效会使马氏体部分分解,造成马氏体逆转变困难。     

Ti50＋x Pd30Ni20—x合金的相变温度

使用热分析和高温X射线研究了Ti50-xPd30Ni20-x合金相变温度的变化情况,发现当Ti的原子分数偏离50%时,合金的相变温度随Ti成分的升高而降低,处于固溶处理的合金的相变温度最高,合金经过轧制及回复处理后,相变温度会降低。分析认为,这与合金内的缺陷、内应力和析出物密切相关。     

Ti（50）Ni（47）Fe3形状记忆合金冷轧变形后的组织与性能

采用拉伸测试、维氏硬度测试、电阻率-温度曲线测试及扫描电镜和透射电镜观察显微组织的方法研究冷轧变形量为25%的Ti50Ni47Fe3合金经450-750°C下1 h退火后的显微组织和性能。结果表明,冷轧变形增强了合金的抗拉强度和屈服强度,冷轧变形后形成的应力场有助于R相变的发生。随着退火温度的升高,合金的抗拉强度和屈服强度下降,伸长率增大;当退火温度高于650°C时,强度和伸长率趋于稳定。电阻-温度曲线表明,在升、降温过程中发生两阶段相变B2-R-B19′。随着退火温度的升高,合金的相变温度降低;当退火温度高于650°C时,相变温度趋于稳定。随着退火温度的升高,合金依次发生回复、再结晶和晶粒长大。     

铁磁性Co-Fe记忆合金的马氏体相变特性及形状记忆效应

采用光学显微镜、X射线衍射、DSC、弯曲试验等方法研究了Co-Fe合金的微观组织结构、马氏体相变特性及形状记忆效应.结果表明:Co-Fe合金的记忆效应源自合金中的fcc/hcp马氏体相变;Co-xFe(x=2%～6%,质量分数)合金在x≥5.65%时为单一fcc结构的y相,在x≤5.6时为含有ε马氏体相和γ相的双相组织;该合金的马氏体相变温度随着Fe含量的增加而线性降低,之间关系为:Ms(℃)=417-69.97x(Fe%);Co-4Fe合金的形状记忆可回复应变最大为0.86%,相信通过进一步的热处理和记忆训练,该合金会表现出更好的记忆效应.     

Ni50Mn27Ga23快淬薄带的马氏体相变和磁感生应变

采用快淬技术制各了非化学计量成分的Ni50Mn27Ga23多晶薄带，对快淬薄带的马氏体相变和磁感生应变进行了研究。结果表明，快淬薄带侄冷却和加热过程中仍然发牛热弹性马氏体相变及逆相变，具有典型的热弹性形状记忆效应，并且比铸态合金具有更大的应变，但是马氏体相变温度下降。快淬工艺在合金内部引入特定的内应力，使薄带形成织构，是合金获得更大相变应变和磁感卞应变的原因。热处理后，内应力大大降低，导致磁感牛应变降低。     

不同固溶处理工艺对Ti50Ni24.9Cu25Y0.1合金组织与相的影响

采用金相显微镜和X射线衍射（XRD）仪研究900 ℃,9 h固溶处理,不同冷却方式对Ti50Ni24.9Cu25Y0.1(at%)合金组织、相的影响,并用电子能谱（EDS）分析合金在凝固过程中的元素分布规律。结果表明,合金在凝固过程中有明显的微观偏析,在晶粒内部为富镍相,晶界为富铜相,在晶界和晶粒内部有小面相生长的纯钛析出物;900 ℃,9 h固溶处理可以明显改善合金的微观偏析。XRD分析表明, 900 ℃,9 h,水冷（WQ）固溶处理后,合金由B19’（单斜结构）相和少量fcc结构的Ti2(Ni,Cu)相组成;900 ℃,9 h,空冷(AC)和900 ℃,9 h,炉冷(FC)固溶处理后,合金由单一的B19’相组成。高温XRD分析表明,合金只发生一阶段的B19’-B2马氏体相变。     

Ni52Mn21+xGa27-x(x=0-5)磁性形状记忆合金的相变

研究了非化学计量成分的多晶Ni52Mn21+xGa27-x(x=0-5)系列合金的热弹性马氏体相变和磁相变.合金的马氏体相变温度Ms随Mn含量的增加而升高,当x＞4时,Ms已经升高到室温以上,而马氏体相变滞后△T随z的增大而减小;合金的磁相变温度TC随z增加而升高,但变化范围不大,在z＞2后,Tc保持在348 K左右.实验获得了一种具有实用前景的合金成分--Ni52Mn25Ga23合金,其马氏体相变温度在室温以上,相变滞后仅为5 K.     

Ni含量和热处理对Ti-Ni形状记忆合金相变和形变行为的影响

用示差扫描量热仪和拉伸试验对比研究了不同温度退火态Ti50.5，Ni49.5、Ti49.8Ni50.2和Ti49.4Ni50.6合金的相变特性和形变行为。中温退火态Ti50.5Ni49.5和Ti49.8Ni50.2合金冷却／加热时的相变类型为A→R→M／M→A（A—母相，R—R相，M—马氏体），Ti49.4Ni50.6合金的相变类型为A→R→M／M→R→A。随Ni含量增加，Ti—Ni合金的相变温度降低，相变热滞增加。随退火温度Tn升高，这3种合金的马氏体相变温度升高，热滞减小；Ti50.5Ni49.5合金的R相相变温度TR恒定不变；Ti49.8Ni50.2和Ti49.4Ni50.6合金的TR先升高后降低。室温下，Ti50.5Ni49.5合金呈现形状记忆效应，Ti49.4Ni50.6合金呈现超弹性，Ti49.8Ni50.2合金呈现形状记忆效应＋超弹性。近等原子比和富镍Ti—Ni合金的形状记忆特性优于贫镍合金。随Ta升高，三合金拉伸曲线的平台应力减小；Ti49.4Ni50.6超弹性合金的滞弹性面积增大，阻尼性增强，能量储存密度和储存效率减小。Ta=673～773K时，Ti—Ni合金的形状记忆特性良好，Ta超过823K后，该特性变差。     

Ni50Ti30Zr20与Ni50Ti50合金摩擦磨损性能对比研究

目的以Ni_(50)Ti_(50)合金为参照物,研究Ni_(50)Ti_(30)Zr_(20)合金的摩擦磨损性能。方法采用非自耗真空电弧熔炼炉炼制Ni_(50)Ti_(30)Zr_(20)合金,在合金铸锭上切取样品,以Ni_(50)Ti_(50)合金为对比样品,通过能谱测试(EDS)、X射线衍射(XRD)、显微硬度(HV)测试、摩擦磨损测试、扫描电镜测试(SEM)和3D形貌测试,分别评价Ni_(50)Ti_(30)Zr_(20)合金与Ni_(50)Ti_(50)合金的成分、相组成、显微硬度、耐磨性、磨痕形貌和磨损体积。结果XRD结果显示,Ni_(50)Ti_(50)和Ni_(50)Ti_(30)Zr_(20)合金室温分别由B2奥氏体和B19’马氏体相组成。显微硬度测试结果表明,Ni_(50)Ti_(30)Zr_(20)和Ni_(50)Ti_(50)合金的显微硬度值分别为(381.64±7.32)HV和(230.58±6.74)HV。从形貌图可以看出,两种合金磨损后,磨痕形貌主要由剥层组成。从磨痕能谱分析得出,摩擦实验后,样品表面O和Si元素含量明显增加。根据摩擦系数曲线和磨痕三维形貌图发现,同样载荷下,Ni_(50)Ti_(30)Zr_(20)合金的摩擦系数和磨损体积均小于Ni_(50)Ti_(50)合金,在载荷为20 N时,Ni_(50)Ti_(30)Zr_(20)合金的磨损体积为0.078 mm~3,Ni_(50)Ti_(50)合金的磨损体积为0.084 mm~3。结论Ni_(50)Ti_(30)Zr_(20)与Ni_(50)Ti_(50)合金的磨损机制均为疲劳磨损,两种合金在摩擦实验过程中均会发生氧化,同时磨球会有部分剥落到合金磨痕剥层中。Ni_(50)Ti_(30)Zr_(20)合金的耐磨性优于Ni_(50)Ti_(50)合金。     

Ni60Ti40合金热压缩变形行为及机理

对Ni60Ti40合金高温变形行为及变形机理进行了研究。通过计算获得了该合金在不同变形工艺下的应变速率敏感性指数m和变形激活能Q的变化规律,分别构建了Prasad、Gegel、Malas、Murty和Semiatin等不同失稳判据下的动态材料模型热加工图及包含位错数量的变形机理图。应用热加工图理论分析了该合金的适合成形加工区和流变失稳区,运用变形机理图预测了该合金高温变形过程中基于柏氏矢量补偿的晶粒尺寸和基于模量补偿的流变应力下的位错演变规律及高温变形机理。     

TiNi合金约束相变行为研究

研究了预变形TiNi合金应变约束态下的相变行为结果表明：7％应变TiNi合金变形后第1次应变约束相变产生的恢复应力最大，逆相变开始温度．As′最高随着约束相变循环次数的增加，合金中引入大量塑性变形，降低了TiNi合金的恢复应变，进而造成TiNi合金约束相变恢复应力最大值逐渐降低，但约束逆相变开始温度．As′从第2次相变循环开始，几乎恢复到合金变形前的原始值，且不随相变循环次数增加而改变。